A single transition state in the reaction of aryl diphenylphosphinate esters with phenolate ions in aqueous solution

1988 ◽  
Vol 110 (6) ◽  
pp. 1890-1895 ◽  
Author(s):  
Nicholas. Bourne ◽  
Edwin. Chrystiuk ◽  
Andrew M. Davis ◽  
Andrew. Williams
Keyword(s):  
Aqueous Solution ◽  
Transition State ◽  
Single Transition

Ligand substitution at five-coordinate copper(II) centres by cyanate, chloride and bromide ions

1980 ◽  
Vol 33 (6) ◽  
pp. 1381 ◽  
Author(s):  
JH Coates ◽  
PR Collins ◽  
SF Lincoln
Keyword(s):  
Aqueous Solution ◽  
Transition State ◽  
Ligand Substitution ◽  
Aqua Ligand ◽  
Stopped Flow ◽  
Bromide Ions ◽  
Ethyl Amine ◽  
Ligand Bond

The substitution of the aqua[tris{2-(dimethylamino)ethyl}amine]copper(II) ion by cyanate, chloride and bromide ions has been studied in aqueous solution by static and stopped-flow spectrophoto-metric techniques. This process is unusually slow for ligand substitution at a copper(II) centre and appears to proceed through an interchange mechanism in which the copper(II)-aqua ligand bond makes a major contribution to the transition state energetics.

Single transition state for sulfonato group (SO3) transfer between pyridine nucleophiles

1985 ◽  
Vol 107 (14) ◽  
pp. 4327-4331 ◽  
Author(s):  
Nicholas Bourne ◽  
Andrew Hopkins ◽  
Andrew Williams
Keyword(s):  
Transition State ◽  
Single Transition

Aminolysis of naphthyl acetates catalyzed by cyclodextrins

1999 ◽  
Vol 77 (5-6) ◽  
pp. 950-959 ◽  
Author(s):  
Oswald S Tee ◽  
Michael J Boyd
Keyword(s):  
Aqueous Solution ◽  
Transition State ◽  
Rate Constants ◽  
Nucleophilic Attack ◽  
Reactivity Ratios ◽  
Aryl Group ◽  
First Order ◽  
Free Amine ◽  
Transition State Stabilization ◽  
Pseudo First Order

The effects of cyclodextrins (CDs) on the rate of nucleophilic attack on 1- and 2-naphthyl acetates (1-NA and 2-NA) in aqueous solution have been investigated. Analysis of the variation of the pseudo-first-order rate constants with [nucleophile] and [CD] affords rate constants for reaction of the nucleophiles with free ester (kN) and with ester bound to the CD (kcN). The reaction of 1-NA and 2-NA with the trifluoroethoxide anion is slowed down by β-CD as the ratios kcN/kN are 0.11 and 0.30, respectively. For reaction with the anion of 2-mercaptoethanol in the presence of α-CD, β-CD, "hydroxypropyl-β-CD" (hp-β-CD) and γ-CD, the reactivity ratios kcN/kN vary between 0.04 and 2.4, ranging from strong retardation to modest catalysis; the retardations arise with β-CD and hp-β-CD, which bind the esters strongly. By contrast, the attack of primary alkylamines is generally accelerated, and in many cases substantially so. For the aminolysis of 1-NA in the presence of β-CD, values of kcN/kN range from 7 to 460, assuming that free amine reacts with CD-bound ester. Alternatively, if the CD-catalyzed reaction involves free ester reacting with CD-bound amine, with rate constant kNc, the ratios kNc/kN vary from 43 to 140. Either way, there is appreciable catalysis of the aminolysis of 1-NA by β-CD. For the aminolysis of 2-NA, the effects are less dramatic: the ratios kcN/kN range from 0.19 to 17, and values of kNc/kN vary from 17 to 110. The reaction of 1-NA with n-hexylamine is also catalyzed by γ-CD. The variations of kinetic parameters with alkylamine chain length suggest that the CD-catalyzed aminolysis basically takes place by the attack of CD-bound amine on the free ester. However, there must be some stabilizing interactions between the aryl group of the ester and the CD during the reaction, since the transition state stabilization is different for 1-NA and 2-NA, as well for other esters.Key words: aminolysis, catalysis, cyclodextrin, ester cleavage, kinetics.

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